Projects will be carried out in a number of areas related functionally, conceptually, or through the experimental approaches. A primary method is the correlation of morphology at light and EM levels with physiological properties determined by a number of intracellular electrode techniques. (Project 1) Electrotonic or gap junctions will be studied in tissue cultured heart, liver and lens, in part to give physiological relevance to biochemical studies in other laboratories. (Project 2) The formation of electrotonic synapses will be followed in culture of mammalian neurons to determine factors involved in junctional expression and relation to processes of chemical transmission. Comparison will be made to in vivo development. (Project 3) permeation through gap junction channels will be studied quantitatively and correlated with electrical measurements to determine mechanisms of ion movement and gating. (Project 4) The voltage dependence of gap junctional conductance will be characterized in normal and experimentally altered cells because of the information revealed about gating mechanisms. The phylogeny of voltage dependence will be explored in hopes of finding clues as to function. (Project 5) The as yet undescribed basis of electrotonic coupling in a number of invertebrates will be sought by freeze fracture techniques. Development of functionally specific junctions in cultures of molluscan neurons will be characterized. (Project 6) The dynamics of gap junction formation and disappearance will be studied by thin section and freeze fracture in a number of physiological and experimental situations. (Project 7) Paralytic and other mutants of Drosophila will be tested for effects on electrotonic coupling. Positive results would allow a wide range of genetic approaches. (Project 8) The giant synapse of the hatchetfish is a central synapse uniquely available for experimentation. The Mauthner mediated escape response exhibits habituation that appears to be mediated by inhibition unlike the well studied case in Aplysia. Analyses of mechanisms at the membrane level is required.